1. Field of the Invention
This invention relates to mechanisms for loading and unloading read/write heads on disks in disk drives.
2. Description of Related Art
Read/write heads in disk drives read or write data by sensing or setting the magnetization of areas on rotating disks. Placing a head closer to a disk during reading and writing reduces the amount of disk area that interacts with the head. This increases data density by reducing the size of the smallest readable and writable areas. Accordingly, in some disk drives, heads fly less than a micron above (or even drag on) the surfaces of rotating disks. This requires that disk and head surfaces be extremely smooth.
A problem with close contact of smooth surfaces is a stiction force that arises because smooth surfaces tend to adhere to each other. The stiction force can cause disk wear which leads to data loss and loss of usable storage area. The stiction force also places drag on a disk drive motor during spin up (acceleration of the disk) which increases necessary start-up torque and can cause spin up failure.
To reduce stiction, some disk drives have stationary loading-unloading mechanisms near the outer edges of disks in the drive. Each loading-unloading mechanism unloads a head by lifting the head away from the surface of a disk, so that the head is away from the disk and does not stick to the disk. Accordingly, the disk can spin up without stiction force while the head is away from the disk.
A problem with a stationary loading-unloading mechanism is the difficulty in aligning the loading-unloading mechanism to the disk within the tolerance permitted between the head and the disk. Alignment increases manufacturing costs and creates possible reliability problems because jarring of the disk drive can change the alignment. Another problem with stationary loading-unloading mechanisms is that when a head is loaded onto a disk after the disk is rotating, the head lands on the surface of the disk, near the outer edge of the disk. Often during landing, the head is not completely parallel with the surface of disk and can damage a landing zone on the disk. A disk drive can either waste disk area near the outer edge of the disk by not storing data in the landing zone or suffer from wear and data destruction which may result from head landings. Loading-unloading mechanisms are needed which do not waste or wear the premium track area at the outer edge of disk and which are easier to align.